| 摘要 |
PROBLEM TO BE SOLVED: To detect gas concentration accurately even when a wide gas concentration detecting range is required. SOLUTION: An A/F sensor 30 outputs a current signal corresponding to the air/fuel ration (gas concentration) upon application of a voltage which can be controlled variably through a bias control circuit 10. A sensor current Ip is taken out, in the form of a voltage signal, through a voltage follower 17 and outputted to an A/D converter 41 having a specified input voltage range (0-5 V). A sensor current detection circuit 15 has two current detection resistors 15a, 15b. A CPU 21 operates a switch circuit 18 depending on the sensor current Ip in order to set the resistance variably through the sensor current detection circuit 15. More specifically, an A/F value detected by the current detection resistors 15a, 15b is outputted through a voltage follower 17 in the stoichiometric neighborhood region and an A/F value detected by the current detection resistor 15a is outputted through the voltage follower 17 in other air/fuel region. |
